1. Field of the Invention
The present general inventive concept relates to a piezoelectric inkjet head, and more particularly, to a piezoelectric inkjet head including a plurality of restrictors to restrain crosstalk.
2. Description of the Related Art
Inkjet heads are devices used to form color images on printing mediums by firing droplets of ink onto a desired region of a corresponding printing medium. Inkjet heads can be classified into two types, which are thermal inkjet heads and piezoelectric inkjet heads, depending on the used ink ejecting method. The thermal inkjet head generates ink bubbles by using heat and ejects the ink by utilizing the expansion of the bubbles, and the piezoelectric inkjet head ejects ink using a pressure generated by deforming a piezoelectric material.
FIG. 1 is a cross-sectional diagram schematically illustrating a general structure of a conventional piezoelectric inkjet head. Referring to FIG. 1, a manifold 2, a restrictor 3, a pressure chamber 4, and a nozzle 5 are formed in a channel plate 1 to form an ink channel, and a piezoelectric actuator 6 is disposed on the channel plate 1. The manifold 2 is a common passage through which ink is supplied from an ink tank (not illustrated) to pressure chambers such as the pressure chamber 4. The restrictor 3 is a passage formed between the pressure chamber 4 and the manifold 2. The pressure chamber 4 is formed to receive ink that is to be ejected. The piezoelectric actuator 6 operates to change the volume of the pressure chamber 4, and thereby, resulting in variations of the pressure in the pressure chamber 4. Thus, ink can be ejected from or introduced into the pressure chamber 4.
Ink channels can be respectively formed of ceramic, metal, or synthetic resin plates so as to be thin, and then, the plates can be stacked to form the channel plate 1. The piezoelectric actuator 6 is formed on the channel plate 1 above the pressure chamber 4. The piezoelectric actuator 6 has a stacked structure formed by a piezoelectric layer and electrodes. The electrodes are used to apply a voltage to the piezoelectric layer. Therefore, a portion of an upper wall of the channel plate 1 forming a top wall of the pressure chamber 4 is used as a vibration plate 1a that is deformed by the piezoelectric actuator 6.
An operation of the conventional piezoelectric inkjet head will now described. When the piezoelectric actuator 6 deforms the vibration plate 1a to reduce the volume of the pressure chamber 4, the pressure in the pressure chamber 4 increases, and thus, ink is ejected to the outside of the pressure chamber 4 through the nozzle 5. When the piezoelectric actuator 6 allows the vibration plate 1a to return its original shape in order to increase the volume of the pressure chamber 4, the pressure in the pressure chamber 4 decreases, and thus, ink is introduced into the pressure chamber 4 from the manifold 2 through the restrictor 3.
FIG. 2 is a perspective diagram illustrating a piezoelectric inkjet head disclosed in Korean Patent Laid-Open Publication NO. 2003-0050477 (U.S. Patent Publication NO. 2003-0112300) filed by the applicant of the present general inventive concept.
Referring to FIG. 2, the piezoelectric inkjet head includes three silicon substrates: an upper substrate 30, a middle substrate 40, and a lower substrate 50 that are bonded to one another. The upper substrate 30 includes a plurality of pressure chambers 32 formed in its bottom surface to a predetermined depth. An ink inlet 31 is formed through the upper substrate 30 and connected to an ink tank (not illustrated). The pressure chambers 32 are arranged in two rows at both sides of a manifold 41 formed in the middle substrate 40. Piezoelectric actuators 60 are disposed on a top surface of the upper substrate 30 to apply driving forces to their respective pressure chambers 32 in order to eject ink from the pressure chambers 32. The manifold 41 formed in the middle substrate 40 is connected to the ink inlet 31 of the upper substrate 30. Restrictors 42 are formed at both sides of the manifold 41, and are respectively connected to the pressure chambers 32 of the upper substrate 30. A plurality of vertical dampers 43 are formed through the middle substrate 40 relatively corresponding to the pressure chambers 32. A plurality of nozzles 51 are formed in the lower substrate 50, and connected to the dampers 43, respectively. Each of the nozzles 51 includes an ink introduction portion 51a and an ink ejection portion 51b. The ink introduction portion 51a is formed in an upper portion of the lower substrate 50, and the ink ejection portion 51b is formed in a lower portion of the lower substrate 50. The ink introduction portion 51a is formed in a reversed pyramid shape by anisotropic wet etching, and the ink ejection portion 51b is formed in a cylindrical shape having a constant diameter by dry etching.
However, in the conventional piezoelectric inkjet head illustrated in FIGS. 1 and 2, when the pressure in the pressure chambers 32 increases by the operation of the piezoelectric actuators 60, some of the ink stored in the pressure chambers 32 flows back to the manifold 41 through the restrictors 42, although most of the ink is ejected from the pressure chambers 32 through the nozzles 51. In addition, pressure waves or vibrations can be transmitted to the nozzles 51 of neighboring pressure chambers 32 together with the back flow of ink, thereby affecting ink ejection characteristics of the nozzles 51 of the neighboring pressure chambers 32. This phenomenon is called crosstalk. The crosstalk results in unstable ink meniscuses in the nozzles 51 of the neighboring pressure chambers 32. Thus, ink droplet speed and volume of the respective nozzles 51 are affected, thereby deteriorating image quality.